The present invention relates to a novel mutant strain obtained by irradiation with X-rays using a soybean strain Bay as a new strain, and a soybean oil of a decreased content of polyunsaturated fatty acids obtained therefrom.
In general, a triacylglycerol which is a main component of fats and oils present in plants, particularly their seeds, is a compound obtained by bonding three fatty acid molecules to one glycerol molecule, and depending on the kind of the bonded fatty acid, physical and chemical properties and nutritive values are different. The composition of the fatty acids is specific to plant species from which they are derived, and therefore, it is impossible to avoid limitation of its use for each plant species.
On the other hand, for suppressing degeneration by oxidation in storage of this plant fat and oil, it is necessary to decrease the content of polyunsaturated fatty acids liable to be oxidized.
It is known that, in a soybean seed, a biosynthesis system of palmitic acid →stearic acid →oleic acid →linolic acid → linolenic acid is present, and conversion from oleic acid into linolic acid is conducted with a microsomal ω-6 fatty acid desaturase enzyme and conversion from linolic acid into linolenic acid is conducted with a microsomal ω-3 fatty acid desaturase enzyme, and that ω-6 and ω-3 fatty acid desaturations with these enzymes are correlated with a plurality of genes, and known that parts of them are controlled by genes at the FAD 2-position and FAD 3-position [Plant Physiol., (1993), vol. 103, pages 467-476 and Theor. Appl. Genet., (1997), vol. 94, pages 356-359].